BAGHDAD, Iraq (CNN) --A letter seeking al Qaeda's help battling the U.S.-led coalition in Iraq, if authentic, could provide a rare look into the inner workings of the the country's insurgency.

The 17-page document, which the U.S. military said it believes was written by Jordanian Abu Musab al-Zarqawi and captured last month with an al Qaeda courier, calls for suicide attacks and car bombings against Shiite targets to promote civil war between Sunni and Shiite Muslims in Iraq.

The letter depicts insurgents who are worried about what effect Iraqi self-rule, scheduled for this summer, will have on their efforts. It also expresses frustration over the lack of cooperation between Iraqis and foreign fighters, the Americans' staying power and the growing solidification of Iraqi security forces

Senior coalition officials said the letter was found on a computer disk captured in January with Hassan Ghul, a man identified as an al Qaeda courier. Ghul identified Zarqawi as the letter's author, one official said. Military officials said they believe the letter was intended for al Qaeda leadership in Afghanistan and is a call for more help and support.

The United States suspects Zarqawi of planning the 2002 killing of a U.S. diplomat in Jordan, and American officials said last month they have mounting evidence that he was involved in a November attack on Italian troops in Nasiriya and the August bombing of U.N. headquarters in Baghdad.

Though not a member of al Qaeda, he is believed to be affiliated with the terrorist network, U.S. officials said.

The coalition translated the letter, which was written in Arabic. CNN obtained parts of the letter from a senior coalition official.

Paul Bremer, U.S. civilian administrator in Iraq, gave copies of the 17-page document to members of the Iraqi Governing Council on Tuesday, his aides said.

The document warns that insurgents "are racing against time" as the United States prepares to hand over control of Iraq. The transfer of power to Iraqis is to take place June 30, according to a coalition handover plan set down in November.

The letter promises "suicide operations" and car bombings, saying that stoking civil war by bringing the Shiites "into the battle ... is the only way to prolong the duration of the fight between the infidels and us."

"Many Iraqis would honor you as a guest and give you refuge, for you are a Muslim brother. However, they will not allow you to make their homes a base for operations or a safe house," the author writes.

In the letter, the author names the insurgency's top four targets as:

• Americans, who, the author writes, "are the biggest cowards that God has created and the easiest target."

• The Kurds in northern Iraq who have been autonomous since the end of the Persian Gulf War in 1991.

• The Iraqi troops and police who are "the eyes, ears and hand of the occupier," according to the author.

• The Shiites, the majority Muslim sect, who make up 60 percent of Iraq's population and who were denied some religious freedoms under Saddam Hussein's rule

The letter takes credit for 25 suicide attacks in Iraq. The author says the "martyrdom operations" targeted Americans, Shiites, police and coalition forces and praised the small but effective foreign fighters.

Document: U.S. troops are 'spread thin'

The author writes that U.S. forces are easy targets "because they are spread thin among the people and because it is easy to get weapons."

However, the writer concludes the United States "has no intention of leaving, no matter how many wounded nor how bloody it becomes. It is looking to a near future, when it will remain safe in its bases."

But the country's topography is a liability for a fight, according to the document.

"We know that there are enough good groups and jihad is continuing, despite the negative rumors," the letter says. "What is preventing us from making a general call to arms is the fact that the country of Iraq has no mountains in which to seek refuge, or forests to hide."

The letter also says the growth of an indigenous police force poses obstacles for the insurgency.

"The problem is you end up having an army and police connected by lineage, blood and appearance to the people of the region," the writer says. "When the Americans withdraw, and they have already started doing that, they get replaced by the agents who are intimately linked to the people of this region."

The author says jihadists must have control in Iraq at least four months before a new government takes power.

"We are racing against time in order to create squads of mujahedeen who seek refuge in secure places, spy on neighborhoods and work on hunting down the enemy," the document says.

The author says the foreign fighters are trying to increase their numbers and are preparing for a media campaign to get out their word.

"We can pack up and leave and look for another land -- just like it has happened in lands of jihad. Our enemy is growing stronger day after day, and its intelligence information increases. By God, this is suffocation! We will be on the roads again. Souls will perish and blood will be spilled. This is, however, exactly what we want.

"We have been hiding for a long time and now we are seriously working on preparing a media outlet to reveal the truth, enflame zeal and become an outlet for jihad in which the sword and the pen can turn into one."